Not Applicable
Field of the Invention
The present invention relates to an electromagnetic radiation lamp, specifically to a high intensity pulsed lamp in which light is generated by an electric discharge along or near the surface of a dielectric material.
Pulsed lamps are used in a wide variety of commercial, military, industrial, academic, medical and environmental applications, including treatment of contaminated water and industrial effluent, disinfection of water, materials and objects, laser excitation, paint stripping, curing, photography, decontamination, strobes, beacons, and the like. In commercial flashlammps stored electrical energy is deposited into a gas between two electrodes enclosed in a transparent envelope. The electrical discharge produces plasma that is a source of radiant energy with a spectrum that can range from the infrared, to the visible and ultraviolet regions of the spectrum. The envelope serves to confine the plasma generated by the electrical discharge. Electrical energy typically is delivered in a pulse to the flashlamp by a capacitor (or capacitors) that has been charged up by a high voltage power supply. The flashlamp is repetitively pulsed to provide throughput for commercial use. Thus the optical pulses from the flashlamp characteristically have a high peak power in a system with a relatively low average power.
The intensity from flashlamps is limited by its envelope, which explodes if the pressure and impulse from the pulsed electrical discharge is too large. Also, the lifetime of the flashlamp depends strongly on its operating level relative to its explosion limit. In many uses it would be advantageous to operate at intensities that are impractical with flashlamps.
The Surface Discharge (SD) is a pulsed lamp that is known in the art but has seen little commercialization. The SD lamp has many of the same generic characteristics described above for flashlamps but circumvents some of the limitations. In an SD lamp the pulsed electrical discharge is along the surface of a dielectric. One such known invention is found in my U.S. Pat. No. 5,945,790, which patent is hereby incorporated herein by reference. The present invention can be used in conjunction with that patent and other known SD sources.
In many commercial applications, SD lamps generate very high intensity light pulses. This is feasible because the light emitting plasma is generated along the surface of the dielectric, so that an envelope is not required to confine the plasma. The pressure pulse generated by the high intensity discharge plasma is unconfined, and decreases as the plasma expands. In SD lamps with a dielectric tube known in the art, the SD lamp has an outer tube with a large enough diameter that by the time the pressure pulse reaches the wall it has decreased below levels of concern for degradation. This implementation is found in applications in which the lamp is immersed in a medium, as in UV, ultra violet, water treatment. However, large diameter high quality fused silica tubes are expensive, the end pieces and seals are practical issues.
In addition, many applications utilize light deposited into a volume for any of a number of processing objectives. It is an object of the present invention to employ processing geometries in conjunction with one or more SD lamps in ways that efficiently utilizes the light output, and, when required, that increases the penetration depth of the light into the volume.
Also, for certain combinations of high intensity and pulse length, material is evaporated from the dielectric. The evaporated material evolves into the light emitting plasma, and may contribute to the spectral output It is an object of the present invention to utilize specific dielectric materials to increase the light output in specific spectral ranges. Also, the evaporation of dielectric material may reduce SD lamp lifetime. It is another object of the present invention to reduce the erosion rate in order to increase lifetime.
In flashlamps known-in-the-art, contaminants are produced by the pulsed electrical discharge which can reduce the useful life of the lamp. It is yet another object of the present invention to reduce contamination in order increase lamp lifetime.
Furthermore, high average power is desirable for many commercial uses, which cause heating that must be controlled. Prior art discloses means for cooling the dielectric from xe2x80x9cinside,xe2x80x9d which increases cooling capability. Nevertheless, it is an object of the present invention to provide supplemental or alternative means of cooling.
Also, the dielectric in tubular surface discharges blocks a portion of the light emitted by the plasma. It is another object of the present invention to reduce fraction of light emitted by the plasma that impinges on the dielectric.
Accordingly, the present invention provides alternative means to operate SD lamps at very high intensity, to reduce the erosion rate of the dielectric, to provide new means for cooling, and to reduce light blockage by the dielectric.
In view of the foregoing background discussion, the present invention provides advantages for SD lamps and lamp systems that may be used separately or in conjunction, depending on the application.
In the present SD invention a light emitting plasma is generated along the surface of the dielectric, so that an envelope is not needed for confining the plasma. The means for enclosing the discharge gas is located well away from the discharge, so that the SD lamp can operate at much higher intensity than flashlamps.
The present invention provides an envelope for a surface discharge that is a combination of a reflector and window. The reflector provides directionality for the light, and may be of any number of shapes, depending on the application. An advantage of the combined reflector and window is that it is less expensive and more practical for many applications.
The present invention also provides reflector-window SD lamps in which the reflector has various shapes, e.g. an elliptical shape when high intensity is needed at a surface, for instance to strip paint, treat coatings and the like. Alternatively, the reflector may have a parabolic shape when uniform intensity is needed or a volume is to be irradiated, for instance to treat water.
The present invention includes using SD lamps with a processing chamber having high reflectivity walls and arranging multiple SD lamps to increase light use efficiency and the penetration depth.
The invention also provides means for reducing the erosion or ablation of the dielectric by employing a high-pressure gas adjacent to the dielectric to promote the recondensation of evaporated material back onto the solid dielectric. In addition, the present invention provides means for reducing gas contamination.
The present invention also provides means for cooling the dielectric material. Gas in the vicinity of the light emitting discharge flows along the surface of the dielectric removing heat from the region. Additionally, perforations or holes in the electrodes can provide a means for the gas to cool hot regions underneath the tips of the electrodes. Also in a preferred embodiment enclosed channels or pathways are formed to carry cooling water to the dielectric.
Also, according to the present invention, a small diameter dielectric tube, such as an optical fiber, may be used. An advantage of this embodiment it that a higher fraction of light emitted from the SD plasma leaves the lamp.